Magnetic levitation track profile steel and preparation method

Abstract

Provided in the present invention are magnetic levitation track profile steel and a preparation method. The profile steel is composed of the following chemical components, in percentage by mass: C: 0.08-0.13%, Si: 0.20-0.50%, Mn: 0.80-1.10%, P≤0.015%, S≤0.010%, Als: 0.020-0.060%, Cr≤0.20%, Cu≤0.20%, Ni≤0.30%, Ti≤0.005%, B≤40 ppm, and H≤1.5 ppm, with the balance being iron and inevitable impurities. A magnetic levitation track is directly rolled by means of a one-step hot-rolling forming process, and the magnetic levitation track has good comprehensive properties including magnetic conductivity, strength, ductility, low-temperature impact toughness, etc. The content of Ti, which is disadvantageous for magnetic conductivity, in the profile steel is significantly reduced, and the content of B is controlled within a small fluctuation range. Small ranges of C and Mn result in an improvement in the toughness of the profile steel in a dead zone of deformation.

Description

A magnetic levitation track steel and its preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310761629.7 filed on June 26, 2023, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to the technical field of metallurgy, and in particular to a magnetic levitation track steel and a preparation method thereof. Background Art

[0004] As an important component of the suspension control of maglev trains, maglev tracks must have sufficient magnetic conductivity and meet structural bearing capacity, which brings challenges to material manufacturing.

[0005] Chinese patent application number CN02136192.4 discloses a soft magnetic structural steel and a manufacturing method thereof, which are used for magnetic levitation tracks and a manufacturing method thereof. The technical solution is: soft magnetic structural steel and a manufacturing method thereof, wherein the constituent elements include: Fe, C, Si, Mn, P, S, Als, Cr, Cu, Ti, N, Ni, and Ca, and the characteristic is that the constituent element Ca can be replaced by REM, and the weight percentages of the constituent elements are: C: 0.010% to 0.040%, Si: 1.0% to 2.0%, Mn: 0.60% to 1.00%, P: ≤0.015%, S: ≤0.005%, Als: 0.005% to 0.020%, Cr: <0.60%, Cu: 0.20% to 0.60%, Ti: 0.005% to 0.02%, N: ≤0.010%, Ni: ≤1.00%, Ca or REM: ≤0.010%, and the rest are iron and unavoidable inclusions. The rolling process involves continuous casting, hot rolling, and normalizing, ultimately producing soft magnetic structural steel plates suitable for use in maglev train track beams in northern China. The steel plates used in this technology are solely for lateral guidance and do not bear the weight of the train as structural components, thus omitting any structural strength or toughness requirements.

[0006] Chinese patent application number CN200410017999.7 discloses a soft magnetic structural steel plate with excellent low-temperature toughness, whose composition is (mass percentage): C 0.010% to 0.040%, Si 0.50% to 1.00%, Mn 1.00% to 1.50%, P≤0.015%, S≤0.005%, Als 0.50% to 1.00%, Cr 0.20% to 0.50%, Cu 0.20% to 0.60%, Ti 0.005% to 0.02%, N 0.001% to 0.008%, Ni 0.30% to 0.80%, Ca 10ppm to 60ppm, and the rest is iron and unavoidable inclusions, Pcm≤0.20%. By optimizing the recrystallization controlled rolling and accelerated cooling processes and the subsequent slow cooling process, the grain size of the finished soft magnetic structural steel plate is kept between 10 and 30 μm, achieving excellent mechanical, electromagnetic, and weldability. This makes it particularly suitable for side guide plates in maglev train tracks that must absorb load, guide, and drive forces. This patent only provides one soft magnetic steel plate. To manufacture maglev tracks, the steel plate must undergo welding, straightening, and machining. These processes are complex, costly, and inefficient, severely restricting its industrial application.

[0007] Chinese patent application number CN201811092935.1 discloses an F-shaped steel for high-magnetic flux density maglev tracks and its production method. The steel comprises the following components and their weight percentages: C: 0.04-0.07%, Si: 0.08-0.20%, Mn: 0.5-0.8%, P ≤ 0.015%, S ≤ 0.015%, Nb: 0.015-0.030%, Als: 0.03-0.05%, with the remainder being Fe and impurities. This invention achieves high magnetic flux density and excellent mechanical properties by designing the steel grade composition and controlling the number and size of inclusion particles during the steelmaking process. This process is combined with high-temperature rapid rolling to achieve solid solution of alloying elements in the steel and promote rapid grain growth. The patent utilizes a high-temperature rapid rolling process to achieve rapid grain growth, resulting in good magnetic conductivity, but poor elongation and low-temperature impact resistance.

[0008] Existing technologies primarily focus on improving and optimizing the magnetic permeability of steel materials, but lack systematic improvements in their combined magnetic permeability and structural load-bearing properties, resulting in certain deficiencies. In particular, once the material is formed into steel, due to the cross-sectional characteristics of the steel and the limitations of cooling conditions, significant reductions in magnetic permeability, strength, elongation, and low-temperature impact toughness occur in the deformation dead zone, making it difficult to achieve good overall performance.

[0009] Therefore, a magnetic levitation track steel and a preparation method are needed.

[0010] Summary of the Invention

[0011] The purpose of the present invention is to provide a magnetic levitation track steel section and a preparation method, which adopts a one-time hot rolling forming process to directly roll out the magnetic levitation track, avoids welding and secondary processing of steel plates, reduces carbon emissions in the track manufacturing process, and has excellent comprehensive properties such as magnetic permeability, strength, elongation and low-temperature impact toughness.

[0012] In order to achieve the above object, the present invention provides the following technical solutions:

[0013] A magnetic levitation track steel section consists of the following chemical components by mass percentage: C: 0.08% to 0.13%, Si: 0.20% to 0.50%, Mn: 0.80% to 1.10%, P≤0.015%, S≤0.010%, Als: 0.020% to 0.060%, Cr≤0.20%, Cu≤0.20%, Ni≤0.30%, Ti≤0.005%, B≤40ppm, H≤1.5ppm, and the remainder being iron and unavoidable impurities.

[0014] Furthermore, in the above-mentioned magnetic levitation track steel, the C extreme difference of the cross section of the steel is ≤0.03%, and the Mn extreme difference is ≤0.05%.

[0015] On the other hand, a method for preparing the magnetic levitation track steel is provided, comprising the following steps:

[0016] Step S1: using converter, LF refining and VD vacuum furnace smelting,

[0017] Step S2: using a continuous casting machine to cast steel billets,

[0018] Step S3: The steel billet is heated, rolled and cooled to form a magnetic levitation track steel section.

[0019] Furthermore, in the above preparation method, in step S1, blast furnace iron accounts for no less than 90% of the raw materials for converter steelmaking, the blast furnace iron is pre-dephosphorized, and a sliding slag blocking device is used during converter tapping.

[0020] Furthermore, in the above preparation method, in step S1, the ladle lining, refined slag and alloy for LF refining are all made of low-Ti and low-B materials, wherein the Ti content is ≤0.02% by mass and the B content is ≤0.02% by mass.

[0021] Furthermore, in the above preparation method, in step S1, during the LF refining process, Al wire is added first, then Ca wire is added, and finally B wire is added.

[0022] Furthermore, in the above-mentioned preparation method, in step S2, the continuous casting tundish of the continuous casting machine is provided with an automatic temperature control device. If the temperature T of the molten steel is within 10°C higher than the liquidus temperature Tl, the cover of the tundish is closed and the molten steel is heated and compensated for the temperature; if the temperature T of the molten steel is more than 20°C higher than the liquidus temperature Tl, the cover of the tundish is opened to dissipate heat, and heating is stopped. The automatic temperature control device controls the temperature fluctuation of the molten steel in the tundish to within 20°C.

[0023] Furthermore, in the above-mentioned preparation method, the continuous casting machine is provided with a crystallizer electromagnetic stirring and an end pressure device to homogenize the molten steel during the solidification process, so that the C range of the ingot cross section is ≤0.04%, and the Mn range is ≤0.06%.

[0024] Furthermore, in the above-mentioned preparation method, in step S3, the heating time of the steel billet is 3 hours to 6 hours, the heating temperature is 1150°C to 1230°C, and an unbalanced compensation zone is provided on the cross section of the billet before the final rolling. The unbalanced compensation zone brings additional deformation to the deformation dead zone of the final rolling pass, and is more than 2% greater than the deformation of other areas.

[0025] Furthermore, in the above-mentioned preparation method, cooling is air cooling to ambient temperature after rolling, the finished product structure is polygonal ferrite and pearlite, and the difference between the grain size of the deformation dead zone and the grain size of other areas on the cross section of the steel section is no more than 1 level.

[0026] Analysis reveals that the present invention discloses a magnetic levitation track steel section and its preparation method. This section utilizes a single hot-rolling process to directly roll out the magnetic levitation track, avoiding welding and secondary processing of steel plates, reducing carbon emissions from the track manufacturing process, and exhibiting excellent overall performance, including magnetic permeability, strength, elongation, and low-temperature impact toughness. The design of the ladle lining, refined slag, and alloy using low-Ti and low-B content materials significantly reduces the Ti content in the steel section, which is detrimental to magnetic permeability, and keeps the B content within a narrow fluctuation range. This aids in the addition of B wire in the later stages of LF refining, stabilizing the B content in the steel. While achieving excellent low-temperature impact performance, it avoids the drawbacks of excessive B addition, such as cracking and reduced fatigue performance. An automatic temperature control device controls temperature fluctuations in the tundish within 20°C, minimizing tundish steel temperature fluctuations and reducing mold steel superheat. This helps mitigate segregation in the billet, minimizes the extreme differences in C and Mn elements, and improves the toughness of the steel section's deformation dead zone. Controlling the H content in the steel section reduces the number of H atoms that aggregate at the source. The design of the non-equilibrium compensation zone and the additional reduction greater than 2% in the billet section before final rolling increases the deformation amount in the deformation dead zone, brings about the grain refinement effect, and transforms the stress state in the deformation dead zone into a compressive stress state, eliminating the H atom aggregation in the deformation dead zone and preventing the decrease in toughness caused by hydrogen-induced cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of this specification, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0028] FIG1 is a schematic diagram of the cross-sectional structure of a steel section according to an embodiment of the present invention.

[0029] FIG2 is a schematic diagram of the cross-sectional structure of a billet before final rolling according to an embodiment of the present invention.

[0030] Explanation of reference numerals: 1 steel section; 11 side leg; 12 web; 13 middle leg; 14 outer flange; 2 deformation dead zone; 3 original cross-sectional shape of billet before final rolling; 4 unbalanced compensation zone. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. Each example is provided by way of explanation of the present invention and is not intended to limit the present invention. Indeed, it will be apparent to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention encompasses such modifications and variations as come within the scope of the appended claims and their equivalents.

[0032] One or more examples of the present invention are shown in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and the description have been used to refer to like or similar parts of the present invention.

[0033] According to an embodiment of the present invention, a magnetic levitation track steel is provided, which is composed of the following chemical components in mass percentage: C: 0.08% to 0.13%, Si: 0.20% to 0.50%, Mn: 0.80% to 1.10%, P≤0.015%, S≤0.010%, Als: 0.020% to 0.060%, Cr≤0.20%, Cu≤0.20%, Ni≤0.30%, Ti≤0.005%, B≤40ppm, H≤1.5ppm, and the rest are iron and unavoidable impurities. The C range of the same cross section of the steel is ≤0.03%, and the Mn range is ≤0.05%.

[0034] The range of variation in the composition detected within a specified area is equal to the difference between the maximum and minimum values. For example, if the carbon contents at five points on the same cross section of a steel section (or ingot) are 0.08%, 0.10%, 0.09%, 0.12%, and 0.11%, respectively, from near the surface to the center, the range of carbon content for that section is 0.12% - 0.08% = 0.04%. A lower range can reduce compositional segregation and improve the overall performance of the deformation dead zone of maglev track steel sections.

[0035] C: C is the most economical element in steel for increasing strength, but as the C content increases, the toughness of the steel deteriorates. For the steel sections involved in this invention, it is important to improve the toughness of the deformation dead zone while also avoiding the problem of excessive steel oxidation and reduced ladle life caused by too low a C content. Therefore, the C content is controlled within the range of 0.08% to 0.13%.

[0036] Si: Si is a necessary deoxidizer during the steelmaking process. A small amount remains in the molten steel after deoxidation and dissolves in the ferrite upon cooling, improving strength. However, excessive Si content can form inclusions, reducing plasticity and fatigue properties. The present invention, taking into account both the need for deoxidation control and strength improvement, controls the Si content within a range of 0.20% to 0.50%.

[0037] Mn: It has a solid solution strengthening effect. In this invention, Mn is used to compensate for the strength loss caused by the reduced C content. A Mn to S ratio greater than 80 significantly reduces cracking in the ingot. However, excessive Mn content increases the remanence of the maglev track, increasing coercivity and increasing train energy consumption. Therefore, the Mn content is controlled within the range of 0.80% to 1.10% in this invention.

[0038] Ti: It is easy to form high melting point inclusions, deteriorate the castability of molten steel, and affect the magnetic permeability. Under the premise of economical production, controlling the content at a low level (≤0.005%) can improve the magnetic permeability.

[0039] B: It has a significant impact on the toughness of steel. While trace additions can significantly improve toughness, additions above 40ppm can lead to a sharp deterioration in low-temperature performance. By adding B and maintaining a stable content, steel toughness can be improved at a lower cost.

[0040] H: For the present invention, since the deformation dead zone of the magnetic levitation track steel corresponds to the center of the ingot, H atoms are easy to gather. In addition to reducing the aggregation of H atoms in the core of the ingot through electromagnetic stirring, controlling the H content in the steel to below 1.5ppm can reduce the number of H atoms in the core of the ingot as a whole.

[0041] AlS: It provides deep deoxidation. Adding Al, in addition to Si deoxidation, can further reduce oxygen content to below 30 ppm. AlS also refines grain size, improving overall steel toughness. Keeping AlS within the range of 0.020% to 0.060% improves toughness without compromising castability.

[0042] Ni: It can lower the ductile-brittle transition temperature of steel, but requires a high addition level (above 6%) to achieve this effect. Ni is expensive, and adding large amounts of Ni to improve low-temperature resistance is cost-uneconomical. This invention, by combining Ni with B, can achieve a stable improvement in low-temperature impact resistance at a relatively low Ni addition level (≤0.30%).

[0043] Cr: It is an inevitable residual element in steel. A high Cr content will change the cooling structure of the steel, generating brittle phases such as bainite and martensite, and reducing low-temperature impact properties. Controlling the Cr content within the required range of the present invention will not have a significant impact on toughness.

[0044] Cu: It is an inevitable residual element in steel. Excessive content will cause surface cracks to appear after the ingot is heated, and will be inherited to the finished product to form surface defects. If the content is controlled within the required range of the present invention, surface crack defects will not be caused.

[0045] As shown in Figure 1, the steel section 1 includes a side leg 11, a web 12, a middle leg 13 and an outer flange 14. One end of the side leg 11 is connected to one end of the web 12, one end of the middle leg 13 is connected to the other end of the web 12, the other end of the side leg 11 and the other end of the middle leg 13 extend to the same side of the web, one end of the outer flange 14 is connected to the other end of the web 12, and the other end of the outer flange 14 extends along the axis of the web 12 in a direction away from the web 12.

[0046] The present invention also discloses a method for preparing the magnetic levitation track steel, comprising the following steps:

[0047] Step S1: using converter, LF refining and VD vacuum furnace smelting.

[0048] Blast furnace hot metal accounts for no less than 90% of the raw materials used in converter steelmaking. Pre-dephosphorization of the blast furnace hot metal is performed, and a sliding slag retainer is used during the converter tapping process. Blast furnace hot metal accounts for no less than 90% of the raw materials used in converter steelmaking, improving steel purity and reducing the presence of harmful elements introduced by scrap steel.

[0049] The ladle lining, refining slag, and alloy used in LF refining all utilize low-Ti and low-B materials, with Ti content ≤0.02% by mass and B content ≤0.02% by mass. During the LF refining process, the use of low-Ti and low-B materials for the ladle lining, refining slag, and alloy significantly reduces the Ti content, an element detrimental to magnetic permeability, in the steel sections, resulting in improved magnetic permeability and keeping the B content within a narrow fluctuation range. This facilitates the accurate addition of B-wire and stabilizes the B content in the later stages of LF refining, achieving excellent low-temperature impact values ​​while avoiding the drawbacks of steel cracking and reduced fatigue performance caused by B addition.

[0050] During the LF refining process, Al wire is added first, then Ca wire, and finally B wire. The Al wire is used to deeply deoxidize the molten steel, and the formed Al2O3 quickly floats to the slag under the action of Ca, which not only reduces the O content but also does not increase the inclusions in the molten steel. The final addition of B wire can minimize the oxidation failure of the B element and the formation of B-containing oxide inclusions, thereby achieving stable control of the B content.

[0051] Step S2: using a continuous casting machine to cast a steel billet.

[0052] As shown in Figure 1, the steel section's deformation dead zone 2 corresponds to the center of the billet, specifically, the location where the web 12 connects to the center leg 13. Existing magnetic levitation track steel sections exhibit severe segregation of elements such as C and Mn, resulting in significantly lower toughness in the dead zone than in other areas. In an embodiment of the present invention, the continuous casting tundish of a continuous casting machine is equipped with an automatic temperature control device, comprising an automatic heating device and a heat dissipation device. If the molten steel temperature T exceeds the liquidus temperature T1 by less than 10°C, the tundish lid is closed and the automatic heating device is used to reheat the molten steel. If the molten steel temperature T exceeds the liquidus temperature T1 by more than 20°C, the tundish lid is opened and the heat dissipation device is used to dissipate heat. The automatic heating device stops heating, and the automatic temperature control device controls temperature fluctuations of the molten steel within the tundish to within 20°C. This configuration minimizes temperature fluctuations of the molten steel in the tundish, reduces mold steel superheat, mitigates billet segregation, and improves the toughness of the steel section's deformation dead zone 2. The continuous casting machine is equipped with a mold electromagnetic stirring and end-stage screw-down device to homogenize the molten steel during solidification, maintaining a cross-sectional carbon range of 0.04% or less and a manganese range of 0.06% or less. This design reduces the carbon and manganese ranges in the slab, further alleviating segregation and improving the toughness of the steel section's deformation dead zone (Zone 2).

[0053] Step S3: The steel billet is heated, rolled and cooled to form a magnetic levitation track steel section.

[0054] The billet is heated for 3 to 6 hours (e.g., 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours) at a temperature of 1150°C to 1230°C (e.g., 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, or 1230°C). An unbalanced compensation zone 4 is provided on the billet cross-section prior to final rolling. As shown in FIG2 , the unbalanced compensation zone 4 is located above the billet in the original pre-final rolling cross-section shape 3. Relative to the finished steel section, the unbalanced compensation zone is located above the web 12 and opposite the center leg 13. The unbalanced compensation zone 4 introduces additional deformation to the dead zone 2 of the final rolling pass, causing the dead zone 2 to exceed the deformation of other areas by more than 2%. The design of heating time and heating temperature can diffuse and homogenize the segregated elements in the steel billet, further improve the composition and uniformity of the deformation dead zone, and make the steel have good magnetic conductivity while improving the overall tensile strength and elongation of the steel.

[0055] The cooling is air cooling to ambient temperature after rolling, and the finished product structure is polygonal ferrite and pearlite. The difference between the grain size of the deformation dead zone and the grain size of other areas on the cross section of the steel section is no more than 1 level. The strain amount of the deformation dead zone rolling process of the steel section in the prior art is very small, the grains are more than 2 levels coarser than other areas of the steel section, and the stress is in a tensile stress state, which causes H atoms to aggregate, resulting in poor toughness of the steel section. In an embodiment of the present invention, the control of the H content of the steel section reduces the number of H atoms aggregated from the source. The design of the non-equilibrium compensation zone 4 of the billet section before final rolling and the additional reduction amount greater than 2% increases the deformation amount of the deformation dead zone 2, brings about a grain refinement effect, and transforms the stress state of the deformation dead zone 2 into a compressive stress state, eliminating the H atom aggregation in the deformation dead zone and preventing the decrease in toughness caused by hydrogen-induced cracks.

[0056] This manufacturing method uses a single hot-rolling process to directly produce the maglev track, eliminating welding and secondary processing of the steel plates. This reduces carbon emissions from the track manufacturing process, streamlines the process, lowers costs, and improves efficiency. The maglev track has a yield strength of ≥270MPa, an elongation of ≥28%, a saturation magnetic flux density (B100) of ≥1.78T, and a low-temperature impact strength of ≥200J.

[0057] It should be noted that the process parameter range upper and lower limits and interval values ​​of the present invention can all realize the present method, and the embodiments are not listed here one by one. The contents not described in detail in the present invention can all be adopted from the conventional technical knowledge in this field.

[0058] Example 1:

[0059] A magnetic levitation track steel section having the following chemical composition by mass: C: 0.08%, Si: 0.50%, Mn: 0.80%, P: 0.013%, S: 0.010%, Al: 0.024%, Cr: 0.1%, Cu: 0.2%, Ni: 0.30%, Ti: 0.003%, B: 30ppm, H: 1.2ppm, with the remainder being iron and unavoidable inclusions. The cross-sectional carbon range is 0.03%, and the Mn range is 0.05%.

[0060] The method for producing the magnetic levitation track steel structure is as follows: steel billets are refined in a converter, LF refining, and a VD vacuum furnace, then cast in a continuous casting machine. The billets are then heated, rolled, and cooled to form the magnetic levitation track steel structure. The LF refining ladle lining, refined slag, and alloy are low in titanium and boron, with a titanium content of 0.02% by mass and a boron content of 0.01% by mass. During the LF refining process, aluminum wire is added first, followed by calcium wire, and finally boron wire.

[0061] The raw material for converter steelmaking is 90% blast furnace iron, which is pre-dephosphorized.

[0062] If the molten steel temperature T is within 10°C higher than the liquidus temperature Tl, the tundish cover is lowered and the molten steel is heated. If the molten steel temperature T is more than 20°C higher than the liquidus temperature Tl, the tundish cover is opened to dissipate heat and the automatic heating device is turned off. The automatic control device keeps the temperature fluctuation of the molten steel in the ladle within 20°C.

[0063] The continuous casting machine is equipped with a crystallizer electromagnetic stirring and terminal pressure device to homogenize the molten steel during the solidification process, so that the C range of the ingot cross section is ≤0.04% and the Mn range is ≤0.06%.

[0064] The billet is heated for 6 hours at a temperature of 1150° C. The non-equilibrium compensation zone is used to provide additional deformation to the dead zone of the final rolling pass, which is 3% greater than the deformation in other areas.

[0065] Cooling is air cooling to ambient temperature. The finished product structure is polygonal ferrite and pearlite. The grain size difference between the deformation dead zone and other areas on the cross section of the steel section is not greater than level 1.

[0066] Example 2:

[0067] A magnetic levitation track steel section having the following chemical composition by mass: C: 0.10%, Si: 0.20%, Mn: 1.0%, P: 0.010%, S: 0.005%, Al: 0.045%, Cr: 0.2%, Cu: 0.1%, Ni: 0.20%, Ti: 0.001%, B: 20ppm, H: 1.0ppm, with the remainder being iron and unavoidable inclusions. The cross-sectional carbon range is 0.02%, and the Mn range is 0.05%.

[0068] The method for producing the magnetic levitation track steel structure is as follows: steel billets are refined in a converter, LF refining, and a VD vacuum furnace, then cast in a continuous casting machine. The billets are then heated, rolled, and cooled to form the magnetic levitation track steel structure. The LF refining ladle lining, refined slag, and alloy are low in titanium and boron, with a titanium content (mass percentage) of 0.01% and a boron content (mass percentage) of 0.02%. During the LF refining process, aluminum wire is added first, followed by calcium wire, and finally boron wire.

[0069] The raw material for converter steelmaking is 92% blast furnace iron, which is pre-dephosphorized.

[0070] The continuous casting tundish is equipped with automatic heating and cooling devices. If the molten steel temperature T is within 10°C above the liquidus temperature Tl, the tundish cover is lowered and the molten steel is heated to provide additional temperature. If the molten steel temperature T is more than 20°C above the liquidus temperature Tl, the tundish cover is opened to dissipate heat and the heating device is turned off. Automatic control devices keep temperature fluctuations within the tundish within 15°C.

[0071] The continuous casting is equipped with a crystallizer electromagnetic stirring and terminal pressing device to homogenize the molten steel during the solidification process, so that the C range of the ingot section is ≤0.04% and the Mn range is ≤0.06%.

[0072] The billet is heated for 3 hours at a temperature of 1230° C. The non-equilibrium compensation zone brings additional deformation to the dead zone of the final rolling pass, which is 5% greater than the deformation in other areas.

[0073] Cooling is air cooling to ambient temperature. The finished product structure is polygonal ferrite and pearlite. The grain size difference between the deformation dead zone and other areas on the cross section of the steel section is not greater than level 1.

[0074] Example 3:

[0075] A magnetic levitation track steel section having the following chemical composition by mass: C: 0.12%, Si: 0.40%, Mn: 0.9%, P: 0.012%, S: 0.007%, Al: 0.055%, Cr: 0.10%, Cu: 0.10%, Ni: 0.20%, Ti: 0.001%, B: 20ppm, H: 1.5ppm, with the remainder being iron and unavoidable inclusions. The cross-sectional carbon range is 0.02%, and the Mn range is 0.02%.

[0076] The method for producing the magnetic levitation track steel structure is as follows: steel billets are refined in a converter, LF refining, and a VD vacuum furnace, then cast in a continuous casting machine. The billets are then heated, rolled, and cooled to form the magnetic levitation track steel structure. The LF refining ladle lining, refined slag, and alloy are low in titanium and boron, with a titanium content (mass percentage) of 0.01% and a boron content (mass percentage) of 0.01%. During the LF refining process, aluminum wire is added first, followed by calcium wire, and finally boron wire.

[0077] The raw material for converter steelmaking is 98% blast furnace iron, which is pre-dephosphorized and a sliding slag stop is used during the steelmaking process.

[0078] The continuous casting tundish is equipped with automatic heating and cooling devices. If the molten steel temperature T is within 10°C above the liquidus temperature Tl, the tundish cover is lowered and the molten steel is heated to provide additional temperature. If the molten steel temperature T is more than 20°C above the liquidus temperature Tl, the cover is opened to dissipate heat and the heating device is turned off. Automatic control devices keep temperature fluctuations within the tundish within 15°C.

[0079] The continuous casting is equipped with a crystallizer electromagnetic stirring and terminal pressing device to homogenize the molten steel during the solidification process, so that the C range of the ingot section is ≤0.04% and the Mn range is ≤0.06%.

[0080] The billet heating time is 5 hours and the heating temperature is 1200° C. The non-equilibrium compensation zone brings additional deformation to the deformation dead zone of the final rolling pass, which is 5% greater than the deformation of other areas.

[0081] Cooling is air cooling to ambient temperature. The finished product structure is polygonal ferrite and pearlite. The grain size difference between the deformation dead zone and other areas on the cross section of the steel section is not greater than level 1.

[0082] Table 1: Properties of the steel sections prepared in Examples 1-3 of the present invention:

[0083] As can be seen from Table 1, the magnetic levitation track steels prepared in Examples 1 to 3 have excellent yield strength, elongation and low-temperature impact toughness, and relatively high saturation magnetic induction intensity, which improves the comprehensive performance of the magnetic levitation track steels as a whole.

[0084] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0085] 1) The magnetic levitation track is directly rolled out using a one-step hot rolling forming process, avoiding welding and secondary processing of steel plates, reducing carbon emissions in the track manufacturing process, and has excellent comprehensive properties such as magnetic permeability, strength, elongation and low-temperature impact toughness.

[0086] 2) The design of using low Ti and low B content materials for the ladle lining, refined slag and alloy significantly reduces the Ti content in the steel, which is detrimental to magnetic permeability, and controls the B content within a smaller fluctuation range. This plays an auxiliary role in adding B wire in the later stage of LF refining and stabilizing the B content in the steel. While obtaining better low-temperature impact properties, it avoids the shortcomings of steel cracks and reduced fatigue performance caused by excessive addition of B.

[0087] 3) The automatic temperature control device controls the temperature fluctuation of the molten steel in the tundish within 20°C, reducing the temperature fluctuation of the molten steel in the tundish and the superheat of the molten steel in the crystallizer, which is beneficial to reducing the segregation of the steel billet, reducing the extreme difference of C and Mn elements, and improving the toughness of the deformation dead zone 2 of the steel section.

[0088] 4) Controlling the H content of the steel reduces the number of H atoms that aggregate at the source. The design of an unbalanced compensation zone and an additional reduction greater than 2% in the billet section before final rolling increases the deformation in the dead zone 2, resulting in grain refinement. It also shifts the stress state in the dead zone 2 to a compressive state, eliminating H atom aggregation in the dead zone and preventing toughness degradation caused by hydrogen-induced cracking.

[0089] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A magnetic levitation track steel, characterized in that: The steel section is composed of the following chemical components by mass percentage: C: 0.08%-0.13%, Si: 0.20%-0.50%, Mn: 0.80%-1.10%, P≤0.015%, S≤0.010%, Als: 0.020%-0.060%, Cr≤0.20%, Cu≤0.20%, Ni≤0.30%, Ti≤0.005%, B≤40ppm, H≤1.5ppm, and the rest is iron and unavoidable impurities.

2. The magnetic levitation track steel according to claim 1, characterized in that: The cross section of the steel has a C extreme difference of ≤0.03% and a Mn extreme difference of ≤0.05%.

3. A method for preparing a magnetic levitation track steel as claimed in any one of claims 1 to 2, characterized in that: The steps include: Step S1: using converter, LF refining and VD vacuum furnace smelting, Step S2: using a continuous casting machine to cast a steel billet, Step S3: The steel billet is heated, rolled and cooled to form a magnetic levitation track steel.

4. The preparation method according to claim 3, characterized in that: In step S1, blast furnace molten iron accounts for no less than 90% of the raw materials for converter steelmaking. The blast furnace molten iron is pre-dephosphorized and a sliding slag blocking device is used during the converter tapping process.

5. The preparation method according to claim 3, characterized in that: In the step S1, the ladle lining, refined slag and alloy of LF refining are all made of low-Ti and low-B materials, wherein the Ti content is ≤0.02% by mass, and the B content is ≤0.02% by mass.

6. The preparation method according to claim 3, characterized in that: In the step S1, during the LF refining process, the Al wire is added first, then the Ca wire is added, and finally the B wire is added.

7. The preparation method according to claim 3, characterized in that: In step S2, the continuous casting tundish of the continuous casting machine is provided with an automatic temperature control device. If the molten steel temperature T is within 10°C higher than the liquidus temperature Tl, cover the tundish and heat the molten steel to compensate for the temperature. If the molten steel temperature T is more than 20°C higher than the liquidus temperature Tl, open the cover of the tundish to dissipate heat and stop heating. The automatic temperature control device keeps the temperature fluctuation of the molten steel in the tundish within 20°C.

8. The preparation method according to claim 3, characterized in that: The continuous casting machine is equipped with a crystallizer electromagnetic stirring and terminal pressing device to uniformly distribute the molten steel during the solidification process. The C range of the ingot section is ≤0.04%, and the Mn range is ≤0.06%.

9. The preparation method according to claim 3, characterized in that: In step S3, the heating time of the steel billet is 3 hours to 6 hours, and the heating temperature is 1150° C. to 1230° C. The section of the billet before the final rolling is provided with an unbalanced compensation area, which brings additional deformation to the deformation dead zone of the final rolling pass and is more than 2% greater than the deformation of other areas.

10. The preparation method according to claim 3, characterized in that: Cooling is air cooling to ambient temperature after rolling. The finished product structure is polygonal ferrite and pearlite. The difference between the grain size of the deformation dead zone and the grain size of other areas on the cross section of the steel section is not more than 1 level.

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